I guess it would be benificial to know what camera you have as well, or are your intentions to merely set the flash off no matter where it is? Perhaps you could give us an example of the specific use once modified.

I guess it would be benificial to know what camera you have as well, or are your intentions to merely set the flash off no matter where it is? Perhaps you could give us an example of the specific use once modified.

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i have two camera
sony cybershot dsc h20 and nikon coolpix p80 both are point and shoot camera and neither have hot-shoe nor external flash support!

From a quick qlance when light fall on a phototransistor, the 556 timer is activated causing a 50ms delay (low) followed by a
250ms (high). It is "somhow" (as I am not sure of this section) processed and causes the SCR to output a 6V pulse. This may be the voltage that causes your Vivitar flash to be triggered. It sounds about the right voltage. In the end, its function is very similar to the circuit that Markd77 posted.